Hot glass, especially when formed into various shapes in the manufacture of glass containers such as bottles, is susceptible to being damaged by contact with glass processing equipment. Most of the equipment with which hot glass comes in contact in the hot end process area during the manufacture of glass bottles is fabricated from metallic materials such as stainless steel and other alloys. However, in certain areas of the hot end processing of glass bottles, it has been found desirable to utilize non-metallic materials such as graphite, asbestos, plastics or carbon fibers.
One such application is in fixtures used to lift hot newly formed bottles from the mold in which they are formed and set them down on an air pad for cooling before being conveyed to the annealing furnace. These fixtures are called takeout jaws or tongs. Since metallic takeout jaws may cause scratching or checking by contact with the hot formed bottles, takeout jaws are frequently fabricated with a non-metallic insert for contacting the hot glass. Checking, which is the formation of imperceptible cracks due to sudden localized heat transfer or thermal shock, can be, thereby, largely prevented and scratching is minimized. This is particularly important in the current production of lighter weight, more fragile bottles which require gentler handling.
Of the materials which have been used as inserts for takeout jaws, the most satisfactory to date has proven to be graphite. Although other non-metallic materials have been used, most such non-metallic materials are not completely suitable for use in lifting the hot containers from the molds. Asbestos, which was used at one time, has proved to be undesirable for safety and environmental reasons. Plastics suitable for use at the high temperatures encountered in the hot end process area must be specially formulated and yet have a relatively short service life. Graphite has been found to possess properties which are particularly adapted for contacting hot glass containers including high strength, resistance to oxidation, non abrasive surface integrity, heat resistance, low porosity and long service life.
One of the disadvantages of the takeout jaws previously available was the frequent need to replace worn parts during the course of use in the bottle-forming machine. This wear was caused largely by the movement of takeout jaw inserts within the jaw. Inserts were commonly held in position by steel detent balls positioned in holes in the takeout jaws. Detent balls were subject to wear and fouling due to the accumulation of grease, oil and foreign matter. The detent balls could hang up in their holes permitting the insert to fall out, causing loss of the insert and loss of production. Detent balls seldom provided tight enough fits of the insert to render the insert immovable within the jaw. Some degree of play between the insert and jaw was therefore almost always present.
Coupled with the fact that jaws having close tolerances could not be readily fabricated from cast bronze, the form of takeout jaws conventionally manufactured, the play between the jaw and insert resulted in wear of the insert, necessitating frequent replacement thereof. In most instances, because of the lack of close tolerances in the takeout jaws, replacement of both inserts from a pair of takeout jaws was necessary.
It would, therefore, be desirable to provide takeout jaws which reduce the wear on inserts and in which the inserts can be readily replaced in the event of wear or damage without having to replace parts of the jaws themselves.